Problem with HW97K
I have a problem with my HW97 and I'm running out of ideas what might be the reason.
My setup: HW97K left hand factory sporter stock, .177, 12ft/lbs, V-Glide bought 07/2012, Steve Pope trigger, softer spring in the cocking lever latch, aluminium handle on the cocking lever.
Machined aluminium 11mm to weaver rail with 0.3° drop comparable to the Steyr rail, low B-Square mounts, Bushnell Elite 8-32x40 with Bushnell custom shop Mil-Dot reticle.
The V-Glide has some dampening material in the front of the piston, acc. to S.P. this was newly introduced around the time I bought my kit.
After fitting the V-Glide in 08/2012 and a short run-in the HW performed flawlessly and with constant velocity and superb accuracy with my testet lot of JSB 8,44gr 4,53. The rifle is capable of 20mm groups at 47m at ideal conditions, probably better, but I'm the limiting factor. I use dots and I didn't remove the caps on the turrets of my bushnell for about 3 months, perfect. The HW shot time after time spot on. End of october with temperatures dropping below 10° I began to realize shifts in the POI. First from one training to the next, then during one training from one shot to the next. The shift is vertically and to compensate I have to make about 20 clicks up or down. Its always this shift, not more or less, not a process of several shots and small shifts. Always one shift, about 35mm off at 40m. The V0 is still constant and OK. The ballistic curve is not effected. After clicking and zeroing in again all my holding points work as usual. Until the next shift...
I've tried the following to find the cause, I've disassembled the rifle and inspected everything, at this time I had about 8000 shots on the V-Glide and everything looked like the day I first put it in the HW. Absolutly no visible wear. I've stored the HW cold so there's no temperature difference from storing to the range. I replaced the Bushnell with a brand new one. I loosend and tightened the bolts on mounts and rail on the range before shooting. I moved the rail forward on the prism so that the rear clamping of the rail reaches over both trigger block and main system tube. I've moved the mounts on the weaver rail from furthest apart to closest. I bought a new one piece Diana mount with 1mm drop. Today finally we had a nice spring day with temperatures up at about 18°, same problem, after it happened, I tapped the back of the system using a piece of wood and a hammer. No change, tried the same from the muzzle side. No change. My last idea was that there might be a shift between system and stock which might affect the tension on the trigger housing. After tapping today without anything happening I guess this is not the problem either.
Please help! A bit desperate here, I find myself thinking about a TX200...